LU87602A1 - PROCESS FOR FORMING A REFRACTORY MASS AND SPRAY LANCE OF A MIXTURE OF PARTICLES - Google Patents

Description

Method of forming a refractory mass and spray lance of a mixture of particles.

The present invention relates to a method of forming a refractory mass on the surface of a substrate, according to which a current comprising an oxidizing gas and a mixture of refractory particles and fuel are projected against this surface. reacts exothermically with the oxidizing gas, giving off sufficient heat to at least partially melt the refractory particles so that they bond to form the refractory mass. The invention also relates to a projection lance comprising a head for projecting a current comprising oxidizing gas as well as a mixture of refractory particles and exothermically oxidizable particles.

A process for forming a refractory mass of the type defined above is illustrated in particular by patents GB 1,330,894 and GB 2,170,191 (Glaverbel). It is sometimes called "ceramic welding". This process is particularly suitable for the in situ formation of a refractory mass on a refractory wall of furnaces or other refractory equipment, with a view to the hot repair of this wall. It is preferably implemented while the wall is substantially at its usual working temperature. It is particularly useful for repairing or reinforcing the walls or wall coverings of glass furnaces, coke ovens, cement kilns or the petrochemical industry, or refractory equipment used in the metallurgy of ferrous or non-ferrous metals . In addition, the repair can be carried out during the operation of the furnace, such as the repair of the superstructure of a glass furnace. This method is also useful for the formation of refractory components, for example for the surfacing of refractory metals or other refractory substrates.

This process is particularly useful for forming a refractory lining on parts of equipment that are especially susceptible to intense erosion. This erosion may be due in particular to mechanical or thermo-mechanical abrasion, or to corrosion in the liquid or gas phase of the material forming the wall, or it may be due to a combination of these actions.

The internal face of the vessel blocks of a glass furnace at the surface of the molten glass bath constitutes a specific example of a refractory surface subjected to a very intense corrosive erosion phenomenon. This face of the tank blocks erodes very quickly to such an extent that half the thickness of the blocks can easily, and relatively quickly, be removed there. This erosion is known by the technical name "saber stroke" . The vessel blocks subjected to very high temperatures, such as the vessel blocks of the melting and refining furnace, are formed from highly refractory materials such as refractory materials containing a high proportion of zirconia. We have to cool them continuously to reduce erosion.

The orifices or ladles for casting molten metals, as used in the steel industry for example, are illustrations of other refractory surfaces subjected to relatively significant corrosive and / or thermo-mechanical erosion. Thermo-mechanical abrasion by metal at very high temperatures erodes the surface of the refractory substrate and it is often necessary to reload this surface or to replace at least part of the refractory substrate. The internal refractory surfaces of converters such as those used in steelworks or in the non-ferrous metal industry are also subject to relatively significant erosion following the mixing of the steel or the metal in formation.

The control of the operating conditions during the implementation of this ceramic welding process requires a certain skill on the part of the operator so that the process leads to the formation of a high quality refractory mass.

One of the objects of the invention is to facilitate the control of the various elements in action in the area of impact of said current on the surface of the substrate.

The present invention relates to a method of forming a refractory mass on the surface of a substrate, according to which a current comprising an oxidizing gas and a mixture of refractory particles and fuel are projected against this surface. reacts exothermically with the oxidizing gas, giving off enough heat to at least partially melt the refractory particles so that they bond to form the refractory mass, characterized in that the said fuel comprises particles of sub-millimeter dimensions d '' at least one element capable of forming a refractory oxide by oxidizing and in that one projects against the surface, at the same time as said current, one or more peripheral gas jet (s) which surrounds (s) ) the impact zone of said current on the surface of the substrate to form a gaseous screen around this impact zone.

The expression "formation of a refractory mass on the surface of a substrate" includes not only the formation of a coating of relatively thin thickness on this surface, with the aim for example of forming a refractory layer of wear or in order to strengthen the surface, but also the formation of a mass having the thickness of a brick or even a block.

The method according to the invention is very surprising in that one might expect, knowing the difficulty of controlling the operating conditions, that the projection of at least one additional gas jet around the impact zone, which is in fact the main area of formation of the refractory mass, disturbs the exothermic reaction which is the basis of this formation.

On the contrary, we actually realized that we thus had, in a completely surprising way, an additional parameter to control, during the implementation of the method according to the invention, the various elements which come into play. clearance in the impact zone to form the refractory mass. There is therefore an additional means of action on the course of the exothermic reaction, which allows better control of the formation of the refractory mass.

We also realized that the gaseous screen made it possible to reduce the influence of the environment on the impact zone. In particular, the impact zone is better protected from the turbulence that can reign in the surrounding atmosphere. In the frequent case where the method is implemented during the operation of the furnace on a wall from which the refractory mass is formed, the impact zone is made more independent of the disturbances created for example by the operation, the stopping or the setting in operation of a burner in the vicinity of the workplace.

In addition, the gas screen makes it easier to confine the mixture of particles, and in particular fuel particles of sub-millimeter dimensions, in the impact zone so as to concentrate the action of the various basic elements to form the refractory mass.

According to the invention, the fuel comprises particles of at least one element capable, by oxidizing, of forming a refractory oxide. These elements can generally oxidize very quickly and therefore give rise to an intense production of heat energy in a relatively small space. This significant release of heat promotes the fusion of refractory particles. This characteristic is associated with the fact that the combustible particles have sub-millimeter dimensions to facilitate the rapidity of oxidation. On the other hand, the mass formed will more easily weld with the substrate on which the projection is carried out, since it is most often a refractory wall. In addition, since the exothermic reaction does not generate unwanted by-products for the refractory material, the atmosphere of the impact zone can be confined by the gaseous screen.

The gaseous screen around the impact zone can for example be formed by several peripheral gas jets which meet only near the impact zone. Preferably, however, the peripheral gas jet (s) form at least one gaseous sheath which surrounds said current along its path towards said impact zone. A protective sheath is thus formed around said current and it is possible to prevent elements , in particular gas, from the ambient atmosphere are entrained in the current with the oxidizing gas and the mixture of particles. The entire zone of exothermic reaction and of projection of the mixture into its carrier oxidizing gas can thus be isolated from the atmosphere to avoid the introduction of any foreign element and disturbing for the exothermic reaction, and the latter can therefore also be better controlled. .

Preferably, the peripheral gas jet (s) are each formed of a jet of non-combustible gas whose temperature is of the same order of magnitude as the temperature of said current before the initiation of the exothermic reaction.

Such a process is quite surprising. One of the permanent concerns when performing a ceramic weld is to prevent the temperature of the impact zone from being too low during the formation of the refractory mass, for example following poor control of the various parameters of the exothermic reaction. For example, an excessively cold impact zone can cause momentary interruptions to the exothermic reaction. It is known in particular that if this temperature is too low, an irregular and uncontrolled porosity is formed in the refractory mass formed which leads to obtaining relatively porous masses, not very resistant to abrasion or to corrosion. This porosity appears particularly if the refractory mass is formed by several passages of the spray lance. The projection, according to the invention, of one or more gaseous peripheral jets of relatively cold non-combustible gas against the surface of the substrate to form a gaseous screen around the impact zone is totally surprising because this projection of gas tends to strongly cool the impact zone and one could therefore expect that this cooling would lead to the formation of a porous mass not very resistant to erosion.

When the impact zone moves over the surface to be treated, at least part of this projection of relatively cold non-combustible gas, in sufficient quantity to form an effective screen around said impact zone, tends to cool the surface treated just before the impact of the weld material. This is totally contraindicated in most welding techniques for. obtaining an acceptable result. The process according to the invention is therefore very surprising.

On the contrary, we have found experimentally that, completely unexpectedly, the additional parameter for controlling the exothermic reaction provided by the implementation of the process according to the invention could allow the formation of dense refractory masses more resistant to erosion than the masses previously formed by ceramic welding processes. This result is very surprising because it goes against the opinion that the skilled tradesman has been forging in this field for many years.

The porosity of the refractory mass formed is in particular one of the essential elements which determine its level of resistance to erosion. The porosity weakens the refractory mass by giving more control to the erosive medium, especially if it is also corrosive. The pores free access paths for the erosive medium, thus making the refractory material more sensitive to erosion because the erosive medium can act inside the mass itself.

The porosity of the refractory mass is also one of the essential elements which determine its level of thermo-mechanical resistance. Indeed, the pores also weaken the mass by the fact that they have no mechanical resistance. They thus create weak points in the mass and even possibly initiations of rupture. This brittleness can be more critical when the refractory mass is at high temperature.

We realized in reality that with the implementation of the method according to the invention, it was possible to have a means of controlling the temperature of said impact zone. It is thus easier to prevent the refractory mass in formation from flowing due to too high a temperature in the impact zone. It is therefore possible to adjust the various parameters to create a very energetic exothermic reaction, which reduces the risk of working in operating conditions that are too cold and the risk of operating irregularities such as the intermittent course of the exothermic reaction, while cooling the impact zone to avoid the flow of the mass in formation. This facilitates the production of a homogeneous weld.

Very advantageous results have been obtained by using for example carbon dioxide or nitrogen as a peripheral gas jet. Preferably, however, the peripheral gas jet (s) comprise oxygen. The gaseous screen can thus additionally provide a reserve of oxygen in the immediate vicinity of the impact zone of said current in order to promote the complete combustion of combustible particles, which improves the homogeneity of the mass "formed.

The peripheral gas jet comprising oxygen may consist of an air jet. It is an inexpensive gas and readily available in large quantities. Preferably, however, the peripheral gas jet (s) are essentially formed of oxygen. The oxidative reserve formed around said impact zone is thus more effective since the oxygen concentration is significantly higher. As a result of the more complete combustion of the fuel, the proportion of fuel to the amount of refractory particles may also be slightly reduced. In addition, as usually the oxidizing gas of the stream comprising the mixture of refractory particles and of fuel is preferably pure oxygen, this gas is therefore readily available on site to form the peripheral gas jet (s) according to the invention without require the storage of another gas. On the other hand, by forming an oxygen screen, it is avoided that foreign gases come to prevent the oxidation of the combustible particles and thus disturb the exothermic reaction.

Preferably, the peripheral gas jet (s) are projected towards the surface with an ejection speed at least equal to the ejection speed of said stream. This characteristic makes it possible to provide the peripheral gas jet (s) with kinetic energy which promotes the formation of an effective gas screen.

Advantageously, the peripheral gas jet (s) are projected towards the surface with a flow rate greater than half, and preferably equal to or greater than two thirds, of the flow rate of oxidizing gas in said stream. This promotes the formation of a relatively thick screen and this feature also combines with a high ejection speed to promote the formation of a very effective screen. We noted for example that, in a completely surprising way given the important cooling generated, one could even obtain refractory masses not very porous and very resistant to erosion by forming a sheath of oxygen around the said current with a flow of oxygen approximately 30 to 50% higher than the oxidizing gas flow rate of said stream, also consisting of oxygen in sufficient quantity to maintain the exothermic reaction.

Preferably, the said element or elements capable of forming a refractory oxide by oxidizing is or are one or more elements chosen from silicon, magnesium, zirconium and aluminum. These elements are able to oxidize quickly, giving off intense heat in a relatively localized space.

Advantageously, said combustible particles have an average dimension of less than 50 μm and preferably less than 15 μm, and at least one maximum dimension of less than 100 μm and preferably less than 50 μm. Combustible particles are thus easily oxidized, which promotes the development of intense heat energy in a small space and the achievement of a good weld of refractory particles between them. The small size of these combustible particles also promotes their complete combustion, and therefore the homogeneity of the mass formed.

The invention extends to a refractory mass obtained by a process as described above and in particular to a highly refractory mass based on zirconia and alumina.

The invention also relates to a projection lance comprising a head for projecting a current comprising oxidizing gas as well as a mixture of refractory particles and of particles exothermically oxidizable, characterized in that the projection head comprises a central nozzle or a group of '' nozzles for projecting the mixture of particles dispersed in the oxidizing gas, peripheral gas projection means surrounding the central nozzle or the group of nozzles for projecting one or more peripheral gas jet (s) around said stream projected by the central nozzle or the group of nozzles, and an external cooling ring.

The lance according to the invention is simple and it makes it possible to easily form a gaseous screen around the impact zone of the current projected by the central nozzle or the group of nozzles on the treated surface. This lance according to the invention provides the operator with an additional control parameter to enable him to produce a quality ceramic weld.

The peripheral gas projection means may include a series of projection orifices arranged all around the central nozzle or group of nozzles. Preferably, the peripheral gas projection means comprise an annular orifice for projecting a gaseous sheath around the said stream projected by the said central nozzle or group of nozzles. It is a simple, easy and effective way to maintain a gaseous sheath around the stream comprising the oxidizing gas and the mixture of particles. The annular opening, as well as the central nozzle if it stops, may have a rectangular or circular section.

Advantageously, the peripheral gas projection means are spaced apart with respect to said central nozzle or group of nozzles. The peripheral gas jet (s) can thus be more easily separated, at least in an area close to the projection head, from the central current comprising the oxidizing gas and the mixture of particles.

Preferably, the annular orifice is kept spaced from the central nozzle or from the group of nozzles by an internal cooling ring. This makes it possible to effectively separate the gaseous sheath from said stream at the outlet of the projection head and to keep this stream sufficiently cold at the outlet of the projection head to avoid any premature combustion. The projection head is better cooled and can therefore stay longer in places with very high temperatures. This device is however very surprising because this additional cooling ring increases the weight of the lance, which tends to make it less manageable. However, we have found experimentally that the lance according to the invention was very advantageous for performing high quality ceramic welders in places with very high temperature.

Preferably, the projection area of the peripheral gas projection means is greater than two thirds and less than three times the area of the central nozzle or the total area of the group nozzles. This allows one or more peripheral gas jets to be projected with sufficient speed and flow to give them one or more kinetic energy which enables them to produce an efficient gas screen.

Preferred embodiments of the invention will now be described by way of example with reference to the appended figures, in which:

Figure 1 shows, schematically, the projection area on the surface of a substrate during the implementation of the method according to the invention;

Figure 2 is a schematic and partial section in a spray lance according to the invention; and

FIG. 3 schematically represents an erosion test carried out on refractory masses.

In FIG. 1, the reference 1 represents a portion of the surface of the substrate on which it is desired to form a refractory mass by projection, against this surface, of a current comprising oxidizing gas as well as a mixture of refractory particles and of fuel . This current meets the surface 1 diagrammatically according to an impact zone 2. According to the invention, one or more peripheral gas jets which surround the impact zone 2 are projected at the same time against the surface 1 to form a gaseous screen around this impact zone 2. In FIG. 1, the intersection of this gaseous screen with the surface 1 is represented diagrammatically by an annular zone 3 which surrounds the impact zone 2 contiguously. It is obvious that in practice the annular zone 3 can be slightly spaced from the impact zone 2, or on the contrary the annular zone 3 and the impact zone 2 can partially interpenetrate.

In FIG. 2, the projection head 4 of the lance 5 comprises a central nozzle 6 for projecting the stream 7 comprising the mixture of particles dispersed in the oxidizing gas. Instead of a single central nozzle 6, the lance may include a group of several nozzles for projecting the current 7. A projection lance comprising such a group of nozzles is for example described and claimed in British Patent No. 2,170 122. The head 4 also comprises, according to the invention, peripheral means for spraying gas. In the embodiment shown in FIG. 2, the peripheral gas spraying means comprise an annular orifice 8 which surrounds, spaced apart, the central nozzle 6 for projecting a peripheral gas jet forming a gaseous sheath 9. The gaseous sheath 9 forms the gas screen 3 ′ which intercepts the surface 1 according to an annular zone 3. In a specific example, the area of the annular orifice 8 is slightly greater than twice the area of the central nozzle 6. The mixture of particles, dispersed in the oxidizing gas, is introduced through the supply tube 10 and the gas of the peripheral gas jet is introduced through the pipe 11. The lance 5 also comprises an external cooling ring 12 with inlet and outlet for cooling water. FIG. 2 also shows a cooling ring 13, with inlet and outlet for cooling water, which keeps the annular orifice 8 spaced from the central nozzle 6. This cooling ring can however be omitted if one desired and replaced by a simple small insert to keep the annular orifice 8 spaced from the central nozzle 6.

FIG. 3 schematically represents an erosion test on a refractory mass. A prismatic rod 14, cut from the refractory mass to be tested, is partially immersed in a bath 15 of molten glass at 1550 ° C. contained in a crucible (not shown). This temperature is higher than the highest temperature usually used for molten glass in a glass furnace. This bar is kept submerged and its degree of wear is observed after 4 pm.

Example 1:

The vessel blocks in the melting tank of a glass furnace must be repaired without cooling the furnace. These blocks are strongly eroded, essentially at the level of the bath of molten glass where the "saber blow" is formed. They are highly refractory electrofused blocks based on alumina and zirconia, the composition of which comprises by weight 50-51% of alumina, 32-33% of zirconia, 15-16% of silica and approximately 1% of oxide sodium and which has a total density of 3.84. To reach this surface, the level of molten glass is lowered by about 20 cm. To carry out the repair, a current comprising oxidizing gas and a mixture of refractory particles and fuel are projected against the hot tank block. A mixture of particles is used comprising: 40-50% of ZrC ^, 38-44% of A ^ O ^, 8-4% of Al and 4-8% of Si, percentages by weight. The silicon particles are grains whose average size is 6 μm and whose specific surface is 5000 cm / g. Aluminum particles are grains with an average size of 5 µm and a specific surface area of 4700 cm / g. The maximum size of the aluminum and silicon particles does not exceed 50 µm. The silicon and aluminum particles burn, giving off enough heat to at least partially melt the refractory particles so that they are welded together. Zirconia refractory particles have an average dimension of 150 µm and alumina refractory particles have an average dimension of 100 µm.

To test the resistance to corrosion by the glass of the refractory mass which will be formed on the surface of the tank blocks of the furnace, a refractory mass is first produced on the surface of a reserve tank block, or d 'A suitable substrate, brought to 1500 ° C in a test oven, by implementing the method according to the invention. For this test, 8% of Si and 4% of Al are used by weight in the mixture.

The mixture of particles dispersed in the oxidizing gas is sprayed by the lance 5 shown in FIG. 2. It is introduced by the supply tube 10. The central nozzle 6 is circular and has an area of 113 mm. The mixture is sprayed at a flow rate of 30 kg / h with oxygen as the oxidizing gas at a rate of 25 Nm / h. The stream 7 comprising the mixture of particles and the oxidizing gas reaches the surface 1 to be treated according to an impact zone 2. According to the invention, a peripheral gas jet is also projected against this surface 1 which forms a gaseous screen 3 'around of the impact zone 2. In this example, the peripheral gas jet consists of pure oxygen projected by the annular orifice 8 3 at a flow rate of 40 Nm / h in the form of a gaseous sheath 9 which surrounds the current 7 along its path from the head 4 of the lance 5 to the impact zone 2 2. The annular orifice 8 has a circular section and it has an area of 310 mm.

During the implementation of the process, the gas screen 3 ’provided an additional means of action on the evolution of the exothermic reaction and the formation of the refractory mass. The exothermic reaction is stable and relatively well defined. The total porosity of the mass formed is 9% and its apparent porosity or open porosity is 1.5%. The apparent density of the refractory mass formed, that is to say the density of the mass with its porosity as it exists, is 3.5. The total density or absolute density of this mass, that is to say the density of the refractory material itself measured on a sample finely ground to eliminate the influence of the pores, is 3.85.

A prismatic bar 14 (FIG. 3) of 20 × 20 × 120 mm is cut from this refractory mass. This test bar is kept partially immersed in a bath 15 of molten glass at 1550 ° C. contained in a crucible (not shown). We observe the degree of wear of this bar after 4 pm.

For comparison, a control sample of identical size was produced which was also kept partially immersed in the same bath of molten glass at the same temperature. To facilitate comparison, the control sample and the test bar have been represented diagrammatically according to a single bar 14 in FIG. 3. The control sample is a prismatic bar which has been cut from a refractory mass formed of the same so that the refractory mass of Example 1 except that the peripheral gas jet was omitted, that is to say a refractory mass formed by a process outside the scope of the present invention. The refractory mass thus formed has a total porosity of 19.7% and an apparent porosity of 3.5%. It has an apparent density of 3.03 and an absolute density of 3.77.

After 16 hours, the rod 14 of the control sample takes a shape represented schematically by the dashed line 16. It can be seen that the submerged portion 17 of the rod 14 has undergone significant corrosion due to its immersion in the glass bath and that the edges of the prism are rounded. It can be seen that the surface 18 of the bath 15 of molten glass has strongly eroded the sample to give it a particular shape in "saber stroke" 19. The diameter of the bar at the center of the "saber stroke" is approximately reduced at a third of its nominal value.

The bar 14 cut from the refractory mass formed by the implementation of the method according to the invention takes, after 16 hours, the form represented by the broken line 20. There is a markedly less erosion of the submerged part. The edges of the prism are very slightly rounded. The "saber blow" 19 is very much less pronounced than for the control sample. The diameter of the bar at the center of the "saber cut" is reduced approximately only to two thirds of its nominal value. The implementation of the method according to the invention therefore made it possible to produce a refractory mass clearly more resistant to erosion than the mass formed by the previous method. The microscopic examination of a section made in this bar also shows that there are practically no residual metallic phases, which shows that the oxidation of metallic particles is practically complete. This aspect is very favorable for a refractory mass which must be in contact with the molten glass because it is known that contact of the metal phases with the molten glass is a possible source of development of bubbles in the glass.

Example 2: As a variant of Example 1, a refractory mass is produced in the same way as in Example 1 except that the oxygen flow rate of the current

O

7 is 30 Nm / h and the oxygen flow rate of the peripheral gas jet 9 is 20 Nm / h. The refractory mass formed has an apparent porosity of 2%, a total porosity of 8.3%, an apparent density of 3.56 and a total density of 3.88.

In this mass, a prismatic bar 14 was cut which was partially immersed in the bath 15 of molten glass contained in the crucible. After 16 hours, the erosion test shows an erosion similar to the mass of Example 1. The bar takes the form shown by the broken line 20. The examination under the microscope of a section made in this bar also shows that 'there are practically no residual metal phases.

Example 3:

A refractory mass was produced in the same way as in Example 1, except that the gaseous sheath 9 was formed of carbon dioxide projected at a flow rate of 20 Nm / h and that the oxygen of the stream 7 was projected at a flow rate 30 Nm '/ h. It was also found that the exothermic reaction was stable and relatively well defined. The refractory mass formed had an apparent porosity of 1.5%, a total porosity of 4.6%, an apparent density of 3.5 and an absolute density of 3.67.

In this mass, a prismatic bar 14 was cut which was partially immersed in the bath 15 of molten glass contained in the crucible.

After 16 hours, the erosion test also shows an erosion similar to the mass of Example 1. The bar takes substantially the shape shown by the broken line 20.

Example 4:

A refractory mass was produced in the same way as in Example 1, except that the gaseous sheath 9 was formed of nitrogen projected at a flow rate of 18 Nm / h and that the oxygen of the stream 7 was projected according to a flow rate of 30 Nm / h. It was also found that the exothermic reaction was stable and relatively well defined. The refractory mass formed had an apparent porosity of 2.5% and an apparent density of 3.5.

In this mass, a prismatic bar 14 was cut which was partially immersed in the bath 15 of molten glass contained in the crucible. After 16 hours, the erosion test also shows an erosion similar to the mass of Example 1. The bar takes substantially the shape shown by the broken line 20.

Example 5:

To carry out a consolidation repair in an oven vault formed of silica bricks at a temperature of approximately 1500 ° C., the following mixture is used: 87% of refractory particles of silica, 12% of combustible particles of silicon and 1% combustible aluminum particles, percentages by weight. The particles of silicon and aluminum each have an average dimension of less than 10 μm, the specific surface of the silicon being 2 2 4000 cm / g and that of aluminum being 6000 cm / g. The maximum size of the aluminum and silicon particles does not exceed 50 µm.

This mixture is sprayed using the process according to the invention. The mixture of particles is introduced with pure oxygen through the feed tube 10, at a rate of 35 kg / h of material and 25 Nm ^ / h of oxygen, to be projected in the form of the stream 7. According to l invention, a peripheral gas jet is also projected against the surface 1 to be treated which forms a gas screen 3 'around the impact zone 2. In this example, the peripheral gas jet consists of pure oxygen projected according to a flow rate of 30 Nm / h in the form of a gaseous sheath 9 which surrounds the current 7 along its path from the head 4 of the lance 5 to the impact zone 2. In the mass formed, there is practically no no overlapping metal.

By way of comparison, a refractory mass was formed by spraying the same mixture as above at the rate of 30 kg / h with the same flow of oxygen T.

25 Nm / h. For this comparison, however, the peripheral gas jet of oxygen was omitted.

During the implementation of the method according to the invention, it was realized that the gas screen 3 'provided an additional means of action to control the formation of the refractory mass which does not exist in the case of the comparison test. On the other hand, the gaseous screen 3 ’isolated the impact zone 2 so that the turbulence of the atmosphere due to the operation of the oven during the repair practically had no effect on the formation of the refractory mass. The exothermic reaction was more stable and better confined, and there were no intermittent operations of the exothermic reaction.

Example 6:

Repair is required in a copper converter in the non-ferrous metallurgical industry. The procedure is the same as for Example 5, except that the mixture has the following composition by weight: 40% of chromium oxide particles, 48% of magnesia particles and 12% of aluminum particles. The aluminum particles have a maximum nominal size of 45 μm and a specific surface greater than 3000 cm / g. The refractory particles all have a maximum dimension of less than 2 mm. This exemplary embodiment also showed that, by implementing the method according to the invention, the gas screen provided an additional means of action to control the progress of the exothermic reaction and the formation of the refractory mass. The exothermic reaction is stable and well confined.

As a variant, the annular orifice 8 of the projection head 4 has been replaced by a series of injectors projecting gaseous jets which join to form the gaseous screen 3 ’. Very good results have also been obtained with this projection lance.

Example 7:

It is desired to form a refractory mass having the composition as close as possible to the basic refractory on a steel converter wall made of magnesia bricks - carbon composed of 90% by weight of MgO and 10% of carbon. The wall is at a temperature of 900 ° C. A mixture of particles comprising carbonaceous particles is projected onto these bricks. The mixture is sprayed at a rate of 500 kg / hour in an oxidizing gas stream containing 70% by volume of oxygen. The mixture has the following composition:

MgO 82% by weight Si 4%

Al 4% C 10%

The silicon particles have an average diameter of 10μ and a specific surface of 5000cm2 / gr. The aluminum particles have an average diameter of 10μ and a specific surface of 8000cm2 / gr. The carbon particles are particles formed by grinding coke and their average diameter is 1.25 mm. The MgO particles have an average diameter of 1mm. According to the invention, a gas screen is formed around the current impact zone comprising the particles dispersed in the oxidizing gas on the wall of the converter by projecting CO2 with a flow rate greater than half the flow rate of oxidizing gas to form a gaseous sheath around the said stream. During the implementation of the process, it was found that the exothermic reaction was stable and well confined. The projected carbon particles do not completely oxidize so that the mass formed contains approximately 5% carbon. Without the gaseous screen formed by the peripheral CC> 2 jet, the mass formed contains only about 3% of carbon.

Claims (17)

1. A method of forming a refractory mass on the surface of a substrate, according to which a current is projected against this surface comprising oxidizing gas as well as a mixture of refractory particles and of fuel which reacts exothermically with the oxidizing gas, giving off enough heat to at least partially melt the refractory particles so that they bind to form the refractory mass, characterized in that the said fuel comprises particles of sub-millimeter dimensions of at least one element capable of forming a refractory oxide by oxidizing and in what is projected against the surface, at the same time as the said current, one or more peripheral gas jet (s) which surround (s) the zone of impact of said current on the surface of the substrate to form a gaseous screen around this impact zone. 2. Method according to claim 1, characterized in that the peripheral gas jet (s) form at least one gaseous sheath which surrounds said stream along its path towards said impact zone. 3. Method according to one of claims 1 or 2, characterized in that the peripheral gas jet (s) are each formed of a jet of non-combustible gas whose temperature is of the same order of magnitude as the temperature of said stream before initiation of the exothermic reaction. 4. Method according to one of claims 1 to 3, characterized in that the peripheral gas jet (s) comprise oxygen. 5. Method according to claim 4, characterized in that the peripheral gas jet (s) are essentially formed of oxygen. 6. Method according to one of claims 1 to 5, characterized in that the peripheral gas jet or jets are projected towards the surface with an ejection speed at least equal to the ejection speed of said stream. 7. Method according to one of claims 1 to 6, characterized in that the peripheral gas jet or jets are projected towards the surface with a flow rate greater than half the flow rate of oxidizing gas in said stream. 8. Method according to claim 7, characterized in that the peripheral gas jet (s) are projected towards the surface with a flow rate equal to or greater than two thirds of the flow rate of oxidizing gas in said stream. 9. Method according to one of claims 1 to 8, characterized in that the said element or elements capable of forming a refractory oxide by oxidizing is or are one or more elements chosen from silicon, magnesium, zirconium and Γ aluminum. 10. Method according to one of claims 1 to 9, characterized in that said combustible particles have an average dimension of less than 50 µm and preferably less than 15 µm, and at least one maximum dimension of less than 100 µm and preferably less than 50 pm. 11. Refractory mass obtained by a process according to claims there 10. 12. A highly refractory mass based on zirconia and alumina obtained by a process according to one of claims 1 to 10. 13. Spray lance comprising a head for projecting a current comprising oxidizing gas as well as a mixture of refractory particles and particles exothermically oxidizable, characterized in that the projection head comprises a central nozzle or a group of nozzles for projecting the mixture of particles dispersed in the oxidizing gas, peripheral means for projecting gas surrounding the central nozzle or the group of nozzles for projecting one or more gaseous jet (s) of periphery (s) around said stream projected by the central nozzle or group of nozzles, and an external cooling ring. 14. Spray lance according to claim 13, characterized in that the peripheral gas projection means comprise an annular orifice for projecting a gaseous sheath around the said stream projected by the said central nozzle or group of nozzles. 15. Spray lance according to one of claims 13 or 14, characterized in that the peripheral gas projection means are spaced apart with respect to said central nozzle or group of nozzles. 16. Spray lance according to claims 14 and 15, characterized in that the annular orifice is kept spaced from the central nozzle or from the group of nozzles by an internal cooling ring. 17. Spray lance according to one of claims 13 to 16, characterized in that the projection area of the peripheral gas projection means is greater than two thirds and less than three times the area of the central nozzle or of the total area of the group nozzles.